Optical pockels voltage sensor assembly device and methods of use thereof

ABSTRACT

An optical voltage sensor assembly includes an input fiber-optic collimator positioned and configured to collimate input light beam from a light source. A crystal material is positioned to receive the input light beam from the light source and configured to exhibit the Pockels effect when an electric field is applied through the crystal material. An output fiber-optic collimator is positioned to receive an output light beam from the crystal material and configured to focus the output light beam from the crystal onto a detector. Methods of using the optical voltage sensor assembly are also disclosed.

This application claims the benefit of U.S. Provisional PatentApplications Ser. No. 62/376,147, filed Aug. 17, 2016; Ser. No.62/450,784, filed Jan. 26, 2017; and Ser. No. 62/468,091, filed Mar. 7,2017 which are hereby incorporated by reference in their entirety.

FIELD

The present technology relates to the field of voltage sensors, and moreparticularly to optical voltage sensor assembly devices utilizing thePockels effect to measure voltage, systems including the optical voltagesensor assembly devices, and methods of use thereof.

BACKGROUND

In recent years, there has been an acute need and demand for highlyaccurate voltage sensors in the electrical power distribution industry.This includes applications in the power grid network, as well those forelectrical substations, transformers, switchgear, and relay monitoring.

Historically, measurement of medium voltage at distribution substationshas been accomplished using iron-core ferro-magnetic voltagetransformers. For instance, technologies such as Rogawski coils (RC),current transformer and power transformer (CT & PT) coils, and inductivevoltage dividers have been used for voltage measurement. Suchtechnologies, however, inherently disturb the Electromagnetic Field(EMF) associated with medium voltage transmission measurement. At best,such electromagnetic methods of measurement actively interfere with thevoltage to be determined, thereby compromising the measurement ofvoltage indirectly. These conventional counterparts also have associatedrisks and danger due to arcing, flash, magnetic saturation, explosions,and catastrophic failure.

Given the challenges inherent to electromagnetic voltage measurementtechnology, optical sensors have been proposed for medium andhigh-voltage environments. Such sensors are immune to electromagneticand radio frequency interference, with no inductive coupling or galvanicconnection between the sensor head on high-voltage lines and powertransmission substation electronics. The wide bandwidth of opticalsensors provides for fast fault and transient detection and powerquality monitoring and protection. Optical sensors can be easilyinstalled on, or integrated into, existing substation infrastructure andequipment such as circuit breakers, insulators, or bushings resulting insignificant space saving and reduced installation costs with noenvironmental impact.

Additionally, with the implementation of a Smart Grid and SmartBuildings, there has also been an acute need and demand for new voltagemonitors, switch gear, and circuit breakers that can deliver real-timevoltage information on low voltage circuits (i.e., <1 kV).

Intelligent switch gear and intelligent circuit breakers will be the keyto fully leveraging the Internet of Things (IoT) in managing energyusage both on the grid and within buildings. Conventional circuitbreakers function by “tripping,” or shutting off, when voltage orcurrent exceed an upper threshold. The tripping is sufficient forprotecting downstream circuitry, machinery, and electronics, but offersno additional control. Intelligent switch gear or circuit breakers, onthe other hand, would be able to do significantly more than this simpleprotection function.

By monitoring voltage, current, volt-ampere reactive (VAR), and totalpower, intelligent switch gear or circuit breakers can be used to ensureoptimal delivery of energy to end-users on the distribution grid. Beyondthe grid, intelligent monitoring technology would have broaderapplications in smart, energy efficient buildings, including office,retail, and industrial buildings, and in transportation systems,including electrical vehicle (EV) charging stations, rail networks, andtransportation vehicles.

One key challenge faced by electricity distributors is deliveringminimum voltage to all end users. For example, in the United States,distributors are required to deliver 120 volts±5% at 60 Hz toresidential users. Thus, residential users must receive between 126 and114 volts, this being termed “utilization voltage.” Given the waydistribution systems are structured, there are drops in thisdistribution service voltage based on distance between the distributiontransformer and the end user. Therefore, in the residential scenario, afirst user closer to the distribution transformer may receive 125 volts,whereas a second user further from that same distribution transformerreceives only 115 volts. In this scenario, it is crucial that the seconduser located further from the distribution transformer receives at least114 volts. While the scenario presented here is for residential users inthe United States, it is similar for other end users, or power users,outside of the United States, where distribution service voltages areoften higher than 120 V (e.g., 208 V, 240 V).

An important emerging principle in energy management is conservationvoltage reduction (CVR). The concept behind CVR is that the distributiontransformers provide the minimal voltage possible such that all users ona distribution line receive at least the minimum distribution servicevoltage (e.g., 114 V for U.S. residential users). Thus, rather thandelivering the maximum 126 V to the first residential users on adistribution line to ensure all receive at least 114 V, with CVRdistribution service voltage is monitored at all users such thatdistribution service voltage can be minimized. Doing so allows foroptimal grid utilization and one study suggests that for each 1%reduction in distribution service voltage, mean energy consumption isreduced by 0.8%. Thus, optical voltage sensors could also be employed inlow voltage applications.

A number of optical voltage sensors that utilize the Pockels effect havebeen described. For example, U.S. Pat. Nos. 5,731,579; 5,939,711; and6,492,800, describe Pockels effect-based voltage sensors that include apolarizer at the input and a beam splitter at the output. Devicesdescribed by these patents have been deployed by a number of utilitiesand found to function well at constant temperature. However, whenexposed to significant temperature, humidity, and environmental weatherswings, these devices were no longer able to accurately monitor voltage.

A major issue in the reliability of optical voltage sensors is theenvironmental stability, particularly sensitivity due to temperature andhumidity of the environment surrounding the optical system or assembly.In previous embodiments of the optical voltage sensors, elaboratepolarization diversity schemes have been proposed and utilized thatinvolve various optical components dedicated to polarizationmanipulation of phase and rotation. However, such polarizationcomponents, such as waveplates, retarders, and beam splitters arefragile and can vary greatly over temperature and environmentalconditions and change the phase of the optical beam and resultantsignal.

Recently, Sima, et al. (2016), “Temperature Characteristics of PockelsElectro-Optic Voltage Sensor With Double Crystal Compensation,” AIPAdvances 6, 055109 (2016) described an electro-optic voltage sensorcomprised of double, or stacked, LiNbO₃ crystals with a complex airspaced polarization diversity scheme. This electro-optic voltage sensorhad improved stability from 0° C. to 50° C., however, even this sensordid not meet the temperature stability requirements necessary formonitoring medium and high voltage transmission lines, which requirestability from −40° C. to +80° C. Thus, there is a need in the art for anext generation optical voltage sensor, capable of maintaining accuratereadings over temperatures ranging from −40° C. to +80° C.

Another key challenge encountered with optical voltage sensor occurswhen optical voltage sensors are used in underground or enclosedsituations where they may be exposed to flooding or other sources ofmoisture. In such situations, the standard materials used in opticalvoltage sensors may be subjected to corrosion, which adversely affectssensor performance and longevity.

The present invention is directed to overcoming these and otherdeficiencies in the art.

SUMMARY

One aspect of the present technology relates to an optical voltagesensor assembly. The optical voltage sensor assembly includes an inputfiber-optic collimator positioned and configured to collimate inputlight beam from a light source. A crystal material is positioned toreceive the input light beam from the light source and configured toexhibit the Pockels effect when an electric field is applied through thecrystal material. An output fiber-optic collimator is positioned toreceive an output light beam from the crystal material and configured tofocus the output light beam from the crystal onto a detector.

Another aspect of the present technology relates to a modular switchgearelbow optical voltage sensor device. The modular switchgear elbowoptical voltage sensor device includes a sensor body having a first endand a second end. The second end includes a sensor cavity configured tohouse an optical sensor crystal and a cable cavity configured to houseone or more fiber optic cables. An internal pickoff rod is located inthe first end of the sensor body. An external pick-off rod is connectedto the internal pickoff rod at a pickoff rod connection point within thesensor body, such that the external pickoff rod and the internal pickoffrod form substantially a right angle. A base cap is configured to beattached to the sensor body. The base cap includes a fiber optic cablestrain relief to allow one or more fiber optic cables to pass from thesensor body, through the base cap, and external to the modularswitchgear elbow optical voltage sensor device.

The present technology advantageously provides an all-optical voltagesensor with minimal to no metallic or ferrous parts that utilizes atotally passive optical sensing function of the EMF. The presenttechnology offers several substantial advantages over traditionaltechnologies for medium (i.e., 1.0 to 46 kVolts) and high voltage (i.e.,greater than 46 kVolts) power distribution network measurements.Examples of the technology may also be utilized in low voltageapplications (i.e., less than 1.0 kVolts).

The technology described relates to an all-optical sensor for detectingand measuring voltage or applied electric field. The voltage imprintspolarized light travelling through a crystal or optical material with anoptical phase difference due to projections of the polarization vectoralong the principal axes of the crystal's index ellipsoid via thePockels effect. The phase difference is detected by linearly polarizingthe input light to the crystal, using an entrance linear polarizer, andanalyzing the output light from the crystal through an exit linearpolarizer (also referred to as an analyzer) that is oriented withnon-zero projections along at least two of the principal axes of theindex ellipsoid having different indices of refraction or relativeoptical phase. Any change or oscillation of the applied electric fieldor voltage across the crystal, therefore, is detected as a modulation ofthe intensity of light exiting the analyzer. By measuring the modulationof this light, the voltage across the crystal, or electric field, can bededuced.

A sensor of the present technology that embodies these advantageousfeatures utilizes the Pockels effect, wherein the dielectricpermittivity of a material is changed in first order due to theapplication of an electric field. A key challenge with optical voltagesensors based on the Pockels effect is maintaining accurate readingsover a range of temperatures and environmental conditions, on highvoltage transmission lines. Such transmission lines, due to theirlocation outdoors, are exposed to large swings in temperature andhumidity, along with other environmental conditions. Because of this, itis important that sensors developed for measuring voltage on medium tohigh voltage transmission lines are stable over temperatures rangingfrom −40° C. to +80° C.

The present technology describes the use of an optical system andmethod, in which, without loss of generality, a Pockels effect crystalor material is the active medium for sensing the electric field.Equivalently, the voltage drop across the crystal can be obtained, andprecisely measured, since the voltage is simply the electric fieldintegrated through the crystal. The method to measure the voltage, orequivalently the electric field, of the present technology includes amethod for converting optical phase due to the Pockels effect into anintensity modulated signal. This method is simple and robust incomparison to all other proposed polarization methods and diversityschemes, or more elaborate interferometric methods of analyses.

Examples of this technology provide a completely passive measurement ofvoltage and current (no electronics at the point of measurement) withhigh reliability and long operational life. Another noted feature isthat signals are transmitted by fiber optics that support long distancetransmission allowing for the service at the base of the power pole withonly a hot-stick for install. This is in contrast to traditionalelectrically based technology where performance can be compromised dueto interference and electrical crosstalk. Additionally, the all-opticalformat of the present technology does not require any additional powertaps from the natural transmission line, and is independent of theelectrical or transmission infrastructure with solar or battery poweronly necessary for the processing electronics that can be situatedremotely at the base of the transmission line tower or power pole oreven further.

In order to minimize or substantially eliminate effects on the opticalsignal due to temperature, humidity, and moisture ingress, the presenttechnology provides an integrated robust design, with all opticalcomponents bonded together with no airspaces. Examples in thistechnology advantageously do not utilize any optical polarizationelements, such as waveplates, retarders, and beam splitters, and insteadrelies on a simple polarizer and analyzer paradigm integrated into theoptical assembly to provide a truly robust optical voltage sensor systemand assembly.

In one example, the present technology provides a modular all-opticalsensor, for detecting and measuring voltage or applied electric fieldspecifically adapted for use in switchgear, wherein it is likely to beexposed to flooding or high moisture situations. The modularity of thesystem allows for it to be easily adapted for use in all elbowconfigurations and T-configurations available for load break and deadbreak products. Thus, the modular all-optical sensor of the presenttechnology provides a one-size fits all solution for use with switchgearand voltage monitoring in ground-based and underground applications,which may be subject to adverse conditions such as flooding or highmoisture environments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial schematic and partial block diagram of an exemplarysystem including an exemplary optical voltage sensor assembly of thepresent technology.

FIG. 2 is a perspective view of an exemplary collimator with a polarizerin front of its clear aperture that may be employed with the opticalvoltage sensor assembly illustrated in FIG. 1.

FIG. 3 is a side perspective view of an exemplary glass collimator blockwith cylindrical bore holes for insertion of the collimators that may beemployed with the optical voltage sensor assembly illustrated in FIG. 1.

FIG. 4 is an exemplary Lithium Niobate crystal with the indicateddirection of propagation of light along the b-axis, the plane ofpolarization of light being defined by the a- and c-axes, and an appliedelectric field along the c-axis.

FIG. 5 is the reduced, contracted matrix of electro-optic Pockelscoefficients and elements for symmetry reduced Lithium Niobate (pointgroup symmetry 3 m).

FIG. 6 is a block diagram of an exemplary sensor computing device foruse in the system illustrated in FIG. 1.

FIG. 7 is another exemplary optical voltage sensor assembly including anembedded fiber optic temperature sensor probe inserted into one of theholes of the collimator block of the optical voltage sensor assemblyshown in FIG. 1.

FIG. 8 shows a method to construct a calibration file and utilize thedata in the file to compensate voltage measurements.

FIG. 9 is a perspective view of a modular optical voltage sensor devicefor use with the optical voltage assembly of the present technology foruse with switchgear elbows.

FIG. 10 is a cross-sectional view of an modular optical voltage sensordevice as shown in FIG. 9;

FIG. 11 is a schematic view the sensor body of the modular opticalvoltage sensor device as shown in FIG. 9 with the elbow portion removed;

FIG. 12 shows an exemplary design for the base cap of the modularoptical voltage sensor device as shown in FIG. 9.

FIG. 13 shows a custom pick-off rod with threaded mounting that providesa solid assembly point for use with the elbow of the modular opticalvoltage sensor device as shown in FIG. 9.

FIGS. 14A and 14B are schematics views of the components of an exemplarylow voltage optical voltage sensor assembly. FIG. 14A is an electricfield sensor, whereas FIG. 14B is a direct contact sensor.

FIGS. 15A and 15B are side views of the sensors illustrated in FIGS. 14Aand 14B. FIG. 15A shows a side view of the internal components in anexemplary configuration. FIG. 15B shows a cutout side view of an encasedembodiment.

FIG. 16 shows an exemplary top view of the present technology in a fullyencased example.

DETAILED DESCRIPTION

The present technology relates to the field of voltage sensors, and moreparticularly to optical voltage sensor assembly devices utilizing thePockels effect to measure voltage, systems including the optical voltagesensor assembly devices, and methods of use thereof.

One aspect of the present technology relates to an optical voltagesensor assembly. The optical voltage sensor assembly includes an inputfiber-optic collimator positioned and configured to collimate inputlight beam from a light source. A crystal material is positioned toreceive the input light beam from the light source and configured toexhibit the Pockels effect when an electric field is applied through thecrystal material. An output fiber-optic collimator is positioned toreceive an output light beam from the crystal material and configured tofocus the output light beam from the crystal onto a detector.

FIG. 1 is a partial schematic and partial block diagram of an exemplarysystem 10 including an exemplary optical voltage sensor assembly 12 ofthe present technology. The system 10 includes the optical voltagesensor assembly 12 coupled to a light source 14, a detector 16, and asensor computing device 18. The system 10 may also include other typesand numbers of elements, components, or devices in other configurations,including additional optics, such as lenses, prisms, or filters, orelectronics, such as additional amplifiers, AC to DC converters, ortransducers, by way of example only. Additional optics may be utilized,by way of example, to redirect, focus, collimate, or filter thewavelength of light with the system. Additional electronics may beutilized, by way of example, to condition the signal from the detector16 to facilitate further processing.

The optical voltage sensor assembly 12 includes an input collimator 20,a collimator block housing 22, a spacer block 24, a crystal material 26,and a retro-prism sub-assembly 28, although the optical voltage sensorassembly 12 may include other types and/or numbers of additionalcomponents or elements in other configurations, such as a temperaturesensor or probe as described below.

The optical voltage sensor assembly 12 provides an electro-optic voltagesensor utilizing the Pockels effect in the crystal material 26 within anapplied electric field or across which there is a voltage drop. ThePockels effect is observed as an intensity modulation of light due tothe relative optical phase of polarized light between projections alongprincipal axes of the index ellipsoid of the Pockels active crystalmaterial 26. A differential phase shift is imprinted on the polarizedlight propagating through the crystal material 26 that is linearlyproportional to the magnitude of the electric field applied or thevoltage drop across the crystal material 26. The optical phase isdetected as only a direct intensity modulation of polarized lightexiting the non-linear optical crystal material 26 through an analyzingpolarizer. The intensity modulation of light is generated using acompact, robust, temperature and environmentally stable arrangement of apolarizer and analyzer system within the optical voltage sensor assembly12.

The input collimator 20 of the optical voltage sensor assembly 12 iscoupled to the light source 14, such that the light source 14 providesan incoherent, coherent, or partially coherent light beam to the inputcollimator 20 as described below. In one example, the input collimator20 is coupled to the light source through a fiber optic cable thatallows the light source 14 to be located remotely from the opticalcomponents of the optical voltage sensor assembly 12. An input polarizeror analyzer may be embedded within, bonded to, or attached to the inputcollimator 20. By way of example, FIG. 2 shows an exemplary inputcollimator 20 with a polarizer 32 in front of its clear aperture thatmay be employed with the optical voltage sensor assembly 12. In oneexample, the polarizer 32 is a linear polarizer having a thickness ofless than about 1.0 mm.

The input linear polarizer 32 is embedded and bonded, contacted,adhered, epoxied, glued, attached, or otherwise integrated in the inputcollimator 20, although the input linear polarizer 32 may also belocated in the collimator block housing 22 in the same manner. In oneexample, the input linear polarizer 32 is positioned and configured sothat the linearly polarized light output from the input linear polarizer32 propagates along one of the principal axes of an index ellipsoid ofthe crystal material 26 or along a linear combination of the principalaxes of the index ellipsoid of the crystal material 26, by way ofexample. The input linear polarizer 32 may further be positioned andconfigured so that the linearly polarized light output from the inputlinear polarizer 32 has a polarization vector of light having a non-zeroprojection. By way of example, the polarization vector of light may bebetween about 22.5 degrees and about 67.5 degrees, with at least twoprincipal axes of the modified index ellipsoid of the crystal material26 in the presence of an external applied electric field, such that thedifference in the indices of the two principal axes is non-zero andcontains a Pockels optical phase term that is proportional to theapplied electric field or voltage drop across the crystal material.

The integration of the polarizer 32 into the input collimator 20 andincorporation of the light polarization and analyzing components into anintegrated solution with surface to surface attachment of all elementsprovides a robust and stable assembly over temperature. The assembly isalso impervious to humidity or moisture and other degradingenvironmental conditions. Alternatively, the polarizer 32 may beincorporated into the collimator block housing 22.

The collimator block housing 22 is configured to provide a housing forinsertion of the input collimator 20 and the output collimator 30,although the collimator block housing 22 may house other elements, suchas a polarizing element by way of example. As illustrated in FIG. 3, aglass or ceramic block may be used for the collimator block housing 22to hold the input collimator 20 and the output collimator 30. Thecollimator block housing 22 includes bore holes 33 for securelyreceiving the input collimator 20 and the output collimator 30 therein.In one example, the input collimator 20 and the output collimator 30 areinserted and embedded, bonded, adhered, contacted, or attached in, or tothe collimator block housing 22.

In one example, the collimator block housing 22 provides a thermalexpansion coefficient similar to the glass material of the inputcollimator 20 and the output collimator 30 and any associatedpolarizers, such as the polarizer 32 shown in FIG. 2 by way of exampleonly. This provides for pointing stability for the light beam deliveredfrom the light source 14 in its path traversing the optical voltagesensor assembly 12 and through the crystal material 26, thereby reducingphase variations that can distort the modulated light intensity.

The collimator block housing 22 provides precise and stableopto-mechanical placement of the input collimator 20 and the outputcollimator 30, so as to ensure beam pointing stability and accuracy. Theinput collimator 20 and the output collimator 30 are embedded into thecollimator block housing 22, which is subsequently attached or bonded tothe spacer block 24 of the optical voltage sensor assembly 12, to attainsuccessful beam propagation and fiber coupling from the input collimator20 to the output collimator 30. The present technology provides for sucha robust placement by inserting and bonding the input collimator 20 andthe output collimator 30 into the collimator block housing 22 that isthen bonded to the spacer block 24 of the optical voltage sensorassembly 12.

The spacer block 24 is coupled to the collimator block housing by way ofexample through an optical adhesive bonding, although other attachmentmechanisms may be employed. In one example, the spacer block 24 isconstructed of glass and located between the collimator block housing 22and the Pockels crystal material 26 provides for a uniform andhomogeneous optical interface, reducing thermal mismatch between thecrystal material 26 and the glass materials. The surfaces of the glassspacer block 24 are flat with minimal curvature and low surfaceroughness in order to provide optimal surfaces for bonding thecollimator block housing 22 assembly with the crystal material 26through the spacer block 24, thereby integrating the optical voltagesensor assembly 12. Bonding the components to the glass spacer block 24minimizes fluctuations due to thermal variation of intrinsicbirefringence in the optical voltage sensor assembly 12.

The crystal material 26 is coupled to the spacer block 24 by way ofexample through an optical adhesive bonding. The crystal material 26provides a Pockels crystal cell that exhibits strong optical phasemodulation under electric field excitation, which requires carefuldesign and fabrication. The requirements for the Pockels cell crystalmaterial 26 are high electro-optic coefficients (pm/V) and a geometricalconfiguration such that the optical phase accumulates as a linearfunction of the optical path length. This would suggest a transversemodulator configuration for the Pockels cell crystal material 26 asopposed to a longitudinal configuration that is independent of length.This requires that the Pockels cell crystal material 26 benon-centrosymmetric. The crystal material 26 may be selected from one ofcrystal point group symmetry 3 m, 42 m, 43 m, m3 m, 4 mm, 2 mm, 23, or∞.

A number of materials may be used for the crystal cell material 26,including but not limited to C₆H₅O₂N,Pb_(0.814)La_(0.124)(Ti_(0.6)Zr_(0.4))O₃ (PLZT), β-Zns, ZnSe, ZnTe,Bi₁₂SiO₂₀, Ba_(0.25)Sr_(0.75)Nb₂O₆, KTa_(0.35)Sr_(0.75)Nb_(0.65)O₃,CsH₂AsO₄, NH₄H₂PO₄, NH₄D₂PO₄, KD₂PO₄, KH₂PO₄, Lithium Niobate (LiNbO₃),LiTaO₃, BaTiO₃ SrTiO₃, Ag₃AsS₃, KNbO₃, electro-optic polymers and othermaterials. In one example, crystalline lithium niobate (LiNbO₃) is thechoice Pockels crystal material 26 due to its low conductivity and thefact that under an electric field, charge carriers migrate to thecrystal boundaries. The Pockels effect response could therefore also beenhanced with metallic coatings. FIG. 4 illustrates an exemplary LithiumNiobate crystal that may be utilized for the crystal material 26. Thepropagation of light from the light source 14 is along the b-axis, theplane of polarization being defined by the a and c axes, and the appliedelectric field along the c-axis. Designated surfaces 34 can bemetallized in order to enhance and make uniform the electric fieldacross the crystal material 26.

As is well known to practitioners in the art, the Pockel's effect is thefirst order response of the impermeability (the inverse of the relativepermittivity) of a material to an electric field. The Pockels effect isgenerally described as a tensor that satisfies symmetry conditions andis non-vanishing only for non-centrosymmetric crystals. The Pockelseffect tensor coefficients can be represented in a reduced contractedform as a 6×3=18 matrix set of values. In the presence of an appliedelectric field E, the index ellipsoid, in a Pockels effect material, isby definition:

$\begin{matrix}{{\sum\limits_{i = 1}^{3}\;\left\lbrack {\frac{x_{i}^{2}}{n_{i}} + {\sum\limits_{j = 1}^{3}\;{\sum\limits_{k = 1}^{6}\;{r_{ki}E_{i}x_{i}x_{j}}}}} \right\rbrack} = 1} & (1)\end{matrix}$Where n_(i), is the refractive index along coordinate axis x_(i) at zeroelectric field, r_(ki) is the contracted Pockels coefficient and E_(i)is the component of electric field along the x_(i) axis. Therefore, inthe presence of an external applied electric field, the index ellipsoidwill in general be modified, distorted, and rotated from that of theoriginal index ellipsoid of the material in absence of the electricfield as denoted by the first three terms of equation (1). Under asuitable principal-axis coordinate transformation, the index ellipsoidcan be transformed to the standard form:

$\begin{matrix}{{\frac{x_{t,1}^{2}}{n_{t,1}^{2}} + \frac{x_{t,2}^{2}}{n_{t,2}^{2}} + \frac{x_{t,3}^{2}}{n_{t,3}^{2}}} = 1} & (2)\end{matrix}$Where, now, the transformed indices (subscript t) are general functionsof the standard indices in the absence of an electric field, the Pockelscoefficients r_(ki), and the electric field components, that isn _(t,i) =n _(t,i)(n _(i) ,r _(ki) ,E _(k))  (3)Light traveling through the crystal material 26 will accumulate opticalphase, in a complex manner, according to the projection of thepolarization vector along the principal axes of the index ellipsoidafter application of the electric field.

A non-limiting example configuration that may be used for the crystalmaterial 26, which is readily available, is the Z-cut form which is oftrigonal 3 m (C3v) crystal symmetry, according to Hermann-Manguincrystal notation, and which like all Pockels effect crystals isnon-centrosymmetric (lacking a center of inversion symmetry). Forcongruent Lithium Niobate, the principal axis symmetry reducedelectro-optic Pockels tensor elements has eight non-vanishing componentswith only four unique values. For a transverse modulator configuration,with light propagating along the c-axis, and E-field along the b-axis,only two of the five non-zero Pockels tensor elements are relevant inthe transformed principal axis index ellipsoid, namely, r₁₃ and r₃₃. Theindex ellipsoid relation, characterized by the ordinary (n_(o)) andextraordinary (n_(e)) refractive indices, is distorted by the Pockelsterms as:

$\begin{matrix}{{{\frac{1}{n_{0}^{2}}\left( {a^{2} + b^{2}} \right)} + \frac{c^{2}}{n_{e}^{2}}} = {1 - {r_{13}{E\left( {a^{2} + b^{2}} \right)}} + {{- r_{33}}{Ec}^{2}}}} & (4)\end{matrix}$

In this case, the optical phase of a polarized plane wave (b-axis) dueto an integrated E-field or equivalent voltage drop across the width (d)of the crystal material 26 and propagation through the crystal material26 (L) is given as:

$\begin{matrix}{\Gamma = {{\frac{2\pi}{\lambda}\left( {n_{e} - n_{0}} \right)L} - {\frac{\pi}{\lambda}\left( {{n_{e}^{3}r_{33}} - {n_{0}^{3}r_{13}}} \right)\frac{L}{d}V}}} & (5)\end{matrix}$

Where λ is the wavelength of light, n_(e), is the refractive index ofthe e-ray, n_(o), is the refractive index of the o-ray, r₃₃ and r₁₃ arethe electro-optic Pockels coefficients, L is the length of the crystalmaterial 26 along the direction of propagation of light, d is the widthof the crystal material 26 across which the voltage drop V(t) due to theexternal electric field applied. Note that we will refer to the firstterm due to pure birefringence (Φ_(B)) and the second term as thePockels term (Φ_(P)). The Voltage drop V(t) is time dependent, forexample, but not limited to Alternating Current (AC) voltage on powerlines, so that a change or oscillation induces a modulation of the phasethat is crucial to the methods and algorithms for determination of V(t)using the optical light. For a transverse modulator, the axes for thee-ray and o-ray are perpendicular to the optical propagation directionof light, so that the half wave voltage is given as:

$\begin{matrix}{V_{\pi} = {\frac{d}{L}\frac{\lambda}{{n_{e}^{3}r_{33}} - {n_{0}^{3}r_{13}}}}} & (6)\end{matrix}$and is determined by the crystal design. In this technology, it wasconvenient to choose d=4 mm, L=6 mm, although other values may beselected. Based on typical values of the electro-optic coefficients thecalculated value of Vπ is approximately 1250 volts in single pass (2500Volts in double pass with L=12 mm).

A simple expression for the optical transmission through the opticalvoltage sensor assembly 12 and the crystal material 26 due to thePockels phase can be represented as:

$\begin{matrix}{\frac{I(t)}{I_{o}} = {\sin^{2}\left\lbrack {{\pi\frac{V(t)}{V_{\pi}}} + \Phi} \right\rbrack}} & (7)\end{matrix}$

Here V(t)=V_(m) sin(ωt+ϕ_(AC)) is in this example, but not generallylimited to, an AC voltage across the crystal, ω=2πϕ_(AC) is the angularfrequency associated with 60 Hz AC line frequency, ϕ_(AC) is the AC linephase shift, and Φ is a total track length optical phase factorassociated with the optical voltage sensor assembly 12 which can containall the non-Pockels dependent phase factors. These include naturalbirefringence, pyroelectric, space charge effects, and thermal expansionof the crystal material 26.

Noting that the overall optical phase factor in equation 7 istemperature dependent and can be taken to be calibration factor C(T),and assuming V_(π) is reasonably large compared to the voltage acrossthe crystal material 26. The voltage can be solved for, generically fromeqn. (7) as:

$\begin{matrix}{{V\left( {t,T} \right)} = {{\frac{V_{\pi}(T)}{\pi}\sqrt{\frac{{Pac}\left( {t,T} \right)}{Pdc}}} - {C(T)}}} & (8)\end{matrix}$where the temperature dependence of the term is explicitly indicated,and the optical beam intensities (P_(ac), P_(dc)) are reinterpreted asoptical AC modulated power on the photodiode and its DC component. Theexplicit inverse trigonometric term expression can be included inequation (8) to increase accuracy of the voltage drop calculation forlarger values of V_(m).

The retro-prism assembly 28 is coupled to the crystal material 26. Theretro-prism assembly 28 is configured to receive light propagatedthrough the crystal material 26 and reflect the propagated light beamtwice back into the crystal material 26, although other configurationsmay be utilized. The retro-prism assembly 28 may have any configurationand made be constructed of any materials suitable to reflect the lightbeam twice back into the crystal material 26.

The output collimator 30 is positioned in the collimator block housing22 to receive light directed by the retro-prism assembly back throughthe crystal material 26, the spacer block 24 and the collimator blockhousing 22. In one example, the output collimator 30 is coupled to thedetector through a fiber optic cable that allows the detector 16 to belocated remotely from the optical components of the optical voltagesensor assembly 12. The output collimator 30 is coupled to the detector16 to provide the polarized light from the crystal material 26 based onthe Pockels effect to the detector 16. An output polarizer or analyzer(in similarity to the input polarizer 32 shown in FIG. 2) can beembedded, bonded, or attached to the output collimator 30, through whichthe light is fiber-optically coupled as it exits the optical voltagesensor assembly 12. Alternatively, an output polarizer or analyzer canalso be attached to other portions or components of the optical voltagesensor assembly 12 through which light passes after exiting the crystalmaterial 26, such as the collimator block housing 22. In one example,the output linear polarizer is oriented with its polarizing axis alongthe direction of the light polarization vector that has non-zeroprojections on at least two principal axes of the index ellipsoid of thePockels active crystal material 26 to induce a phase difference in thelight field amplitude such that the exit light intensity is modulated orvaries periodically.

Light source 14, in one example, may be any suitable laser diode thatproduces a temporally or spatially coherent, or partially coherent,light beam, such as a He Ne gas laser operating at a wavelength ofapproximately 632 nm. Alternatively, other laser diodes, operating atother wavelengths, such as 1310 or 1550 lasers, may be utilized. Inanother example, light source 14 may be a non-coherent source, such as alight emitting diode or superluminescent diode by way of example only,coupled with optics or filters to spectrally narrow the linewidth orspatially filter the emitted light beam.

The detector 16 is positioned to receive light beams reflected backthrough the crystal material 26 by the retro-prism assembly 28 throughthe output collimator 30. The detector 16 is configured to measure theoptical phase of the product light beams from which the voltage of theapplied field can be determined as described above. The detector 16 maybe any suitable detector configured to measure the optical phase of thereceived light beam. The detector 16 may be coupled to additionalelectronics, such as an amplifier by way of example only, to prepare thesignal from the detector 16, i.e., the measured optical phase of theproduct light beams, for further processing, although other electronicsmay be utilized to adjust the output signal.

The detector 16 is coupled to sensor computing device 18. Referring nowmore specifically to FIG. 6, sensor computing device 18 is configured todetermine a voltage based on the optical phase of the light as measuredby the detector 16 in accordance with the methods described herein. Thesensor computing device 18 includes processor 38, memory 40,communication interface 42, input device 44, and display device 46,which are coupled together by bus 48 or other communication link,although other numbers and types of systems, devices, components, andelements in other configurations and locations can be used.

The processor 38 executes a program of instructions stored in the memory40 for one or more aspects of the present technology. Other numbers andtypes of systems, devices, components, and elements in otherconfigurations and locations can be used to execute the program ofinstructions stored in the memory 40.

The memory 40 stores these programmed instructions for one or moreaspects of the present technology, although some or all of theprogrammed instructions could be stored and/or executed elsewhere. Avariety of different types of memory storage devices, such as a randomaccess memory (RAM), read only memory (ROM), hard disk, CD ROM, DVD ROM,or other computer readable medium which is read from and written to by amagnetic, optical, or other reading and writing system that is coupledto the processor 38, can be used for the memory 40.

The communication interface 42 is used to operatively couple andcommunicate between the sensor computing device 18 and one or more othercomputing devices via a communications network. Other types and numbersof communication networks or systems with other types and numbers ofconnections and configurations can be used for communication between thesensor computing device 18 and one or more other computing devices. Byway of example only, the communications network could use TCP/IP overEthernet and industry-standard protocols, including NFS, CIFS, SOAP,XML, LDAP, and SNMP. Other types and numbers of communication networks,such as a direct connection, a local area network, a wide area network,modems and phone lines, e-mail, and wireless communication technology,each having their own communications protocols, can be used by thecommunication networks.

The input device 44 and the display device 46 of the sensor computingdevice 18 enable a user to interact with the sensor computing device 18,such as to input and/or view data and/or to configure, program, and/oroperate the sensor computing device 18, by way of example only. Theinput device 44 may include a keyboard, computer mouse, and/or touchscreen, and the display device 46 may include a computer monitor. Othertypes and numbers of input devices and/or display devices could also beused in other examples.

An exemplary operation of the system including the optical voltagesensor assembly 12 will now be described. Light from an incoherent,coherent, or partially coherent light source 14 is delivered by theinput fiber collimator 12, which is inserted into the collimator blockhousing 22. In one example, referring to FIG. 2, the light travelsthrough the polarizer 32 before being introduced into the spacer block24 and into the crystal material 26. The beam of light is thus linearlypolarized before entering the crystal material 26 along the direction ofthe crystal optic axis (b-axis) as shown in FIG. 4. The polarizationstate has a non-zero projection with the a-axis and c-axis, and ideallyfor the case of Lithium Niobate is at 45 degrees with respect to thethese axes.

The polarized light beam is reflected twice by the specially designedretro-prism assembly 28, and re-enters the crystal material 26 again.Based on the Pockels effect, with an electrical field applied to thecrystal material 26, an optical phase is imparted to the light, which isthen, in general, elliptically polarized. Upon exiting the crystalmaterial 26, the light with imparted optical phase is incident on theoutput polarizer, or analyzer, which may be located in the outputcollimator 30 or within the collimator block housing 22.

The orientation of the analyzer ideally is coincident with thepolarization vector of the light producing maximum modulation of lightassociated with the time dependent electric field applied across thecrystal material 26. For Lithium Niobate in a transverse modulatorconfiguration (equation 8, supra), this corresponds to the semi-majoraxis of the outgoing elliptically polarized light. The detector 16measures the imparted optical phase. The sensor computing device 18 thencomputes a voltage based on the optical phase measured by the detector.

FIG. 7 is a perspective view of the exemplary optical voltage sensorassembly 12 illustrated in FIG. 1 with an embedded temperature sensor 50or probe. The structure and operation of the optical voltage sensorassembly 12 in this example is the same as discussed with respect toFIG. 1 except as described below.

It is noted that light traversing through the crystal material 26 with aresponsive Pockels effect experiences a phase modulation in the presenceof an electric field or voltage difference across the dimensions of thecrystal material 26. For the Pockels effect optical voltage sensorassembly 12, the magnitude and intensity of the phase modulation isaffected by the temperature of the material through the dependence ofthe refractive indices and electro-optic Pockels tensor coefficients ontemperature. In addition, the Pockels effect may be combined or maskedby the effects of temperature on birefringence that also affects thephase of the light beam. In order to determine the strength of anexternally applied electric field or voltage, these temperature effectsmust be considered and measured, and a calibration and/or compensationprocedure that corrects for temperature variation must be formulated andapplied for the Pockels effect optical voltage sensor assembly 12. Thisissue is not adequately addressed by the current state of the art andcan be problematic for achieving accurate and repeatable determinationsof voltage measurements using Pockels effect sensors, such as opticalvoltage sensor assembly 12.

Referring now to FIG. 7, in one example, the optical voltage sensorassembly 12 includes a temperature sensor 50. The temperature sensor 50can be attached, embedded, or otherwise coupled to the Pockels effectcrystal material 26. Alternatively, the temperature sensor 50 can beattached, embedded, or otherwise coupled to an optical assembly housingthe Pockels effect crystal material 26. In yet another example, thetemperature sensor 50 is located in proximity to, or within the ambientenvironment of, the Pockels effect optical voltage sensor assembly 12.

By way of example only, the temperature sensor 50, or probe, can be anelectrical, optical, or mechanical temperature sensor. Without loss ofgenerality, examples of temperature sensors or probes that may beutilized with the present technology include optical temperaturesensors, such as by way of example only a GaAs bandgap fiber-optictemperature sensor, fluorescence fiber-optic temperature sensors,electrical temperature sensors such as thermocouples or thermistors, ortemperature dependent driven mechanical flexures or MEMs temperaturesensors, although other types of temperature sensors that could be usedwith Pockels effect optical voltage sensor assembly 12 for the purposesof temperature compensation or calibration. The temperature sensor 50may be communicatively coupled to the sensor computing device 18 toprovide temperature readings that may be used to provide temperaturebased calibration of the voltage measurements determined in the methodsdescribed above.

FIGS. 8A and 8B illustrate an exemplary method or algorithm forcompiling and computing an additive calibration factor based onmeasurement at controlled temperatures using the temperature sensor 50.As shown in FIG. 8A, a calibration factor C(T) is computed at a numberof controlled temperatures T from the measured value of the voltagepotential V(T) over the optical voltage sensor with respect to anapplied known voltage reference Vref. The calibration factor maysubsequently be used for correcting or improving the accuracy orprecision of a voltage measurement V(T) by the optical voltage sensorassembly during operation at an arbitrary measured temperature T, as inFIG. 8B. As shown in FIG. 8B, the voltage calibration C(T), factor isapplied, via functional interpolation, or a lookup or indexed table ofvalues, to the measured voltage V(T) resulting in a corrected voltagereading VC(T) at the measured temperature T. It is to be understood thatthis is but one possible example of the temperature compensation orcalibration method or algorithm, and that other substantial methods,algorithms, flow charts, software or firmware, or reduced instructionscan be devised or formulated based on additive, summative, ormultiplicative corrective or calibration factors based on temperature.

Another aspect of the present technology relates to a modular switchgearelbow optical voltage sensor device. The modular switchgear elbowoptical voltage sensor device includes a sensor body having a first endand a second end. The second end includes a sensor cavity configured tohouse an optical sensor crystal and a cable cavity configured to houseone or more fiber optic cables. An internal pickoff rod is located inthe first end of the sensor body. An external pick-off rod is connectedto the internal pickoff rod at a pickoff rod connection point within thesensor body, such that the external pickoff rod and the internal pickoffrod form substantially a right angle. A base cap is configured to beattached to the sensor body. The base cap includes a fiber optic cablestrain relief to allow one or more fiber optic cables to pass from thesensor body, through the base cap, and external to the modularswitchgear elbow optical voltage sensor device.

Referring now to FIGS. 9-13, a modular optical voltage sensor device 100that may incorporate an example of the optical voltage sensor assembly12 described above in accordance with the present technology for usewith switchgear elbows is described. The modular optical voltage sensordevice 100 includes an elbow cover 101, a sensor body 102, and a basecap assembly 103, although the modular optical voltage sensor device 100may include other type and/or numbers of elements or components in othercombinations. As used here in switchgear refers to an apparatus used forswitching, controlling, and protecting the electrical circuits andequipment from faults. Specifically the switchgear referenced hereincomprises the optical voltage sensor device 100 to monitor electricaldistribution and detect faults. A switchgear is typically found inelectrical substations and is often found at ground level or undergroundwhere the switchgear may be exposed to flooding or similar eventswherein the sensor may become submerged underwater.

The technology described relates to an application for all-opticalsensor for detecting and measuring voltage or applied electric field oncommercial switchgear. This is a unique application since the sensormust be capable of operating in conditions that may include flooding orsimilar exposure to water over a long period. Thus, the sensor must behoused in modular assembly as described below.

In this example, the elbow cover 101 is a commercially available elbowcover that is configured to be mated with the sensor body 102. Referringmore specifically to FIG. 10, the elbow cover 101 includes a conductiveexternal pick-off rod 108 and a conductive internal pick-off rod 110that connect at a pick-off rod connection 112. The external pick-off rod108 and the internal pick-off rod 110 interconnect at a right angle andserve to channel high voltage into the sensor body 102. As used herein,a pick-off rod refers to a conductive material that has a physicalconnection between the high voltage electricity source of the switchgearthat generates an electric field between the tip of the pick-off rod andto the crystal material of the optical voltage sensor assembly, such asthe optical voltage sensor assembly 12 as described above.

The sensor body 102 is formed of an epoxy, although other materials maybe utilized. The sensor body 102 is configured to encapsulate thecomponents of the optical voltage sensor assembly 12 of the presenttechnology as described above, and provides a watertight system forprotecting the optical components of the optical voltage sensor assembly12. The sensor body 102 serves as an electrical insulator and comprisesa ground cage 112 and a preformed cavity 114 to accommodate the voltagesensor crystal (not shown), such as the crystal material 26 as describedabove. The present technology forms an application, which preciselymounts the position of the internal pick-off rod 110 in relation to theground cage 112 and the preformed sensor cavity 114. Referring now toFIG. 11, an electrical connection point with threaded mounting hole 116and an external pick-off rod connection 118 are provided, which togetheract to hold the external pick-off rod 108 in place with the internalpick-off rod 110 as shown in FIG. 10. A sealing gasket 120 is positionedaround the external pick-off rod connection 118 adjacent to the narrowend of the electrical insulator sensor body 102. Referring to FIG. 13,the custom internal pick-off rod 110 is shown, which includes theelectrical connection point with threaded mounting hole 116 thatprovides a solid assembly point for connection with the externalpick-off rod 108, as shown in FIG. 10, for use with the elbow. Thesensor body 102 precisely aligns the elbow mounting post 116.

The base cap 103 is configured to close off the body of the sensor body102 and to provide a solid support for a fiber management, watertightcable fitting 104 and grounding. In one example, the base cap 103 iscomposed of silicon bronze to reduce corrosion, although other materialsmay be utilized. The base cap 103 connects to the insulator sensor body102 and serves as an electrical low potential connection point. The basecap 103 further serves as a watertight entry point for optical fibercabling through watertight cable fitting 104 and provides strain relief.Referring more specifically to FIG. 12, the conductive base cap 103includes a gasket sealing area 128 as well as an integrated ground lugmounting 130. The base cap 103 coupled to the sensor body 102 serves asan electrical low potential connection point and provides an attachmentpoint for the fiber optic cable strain relief through which fiber opticcables 122 pass. In this example, the fiber optic cables 122 passthrough a second fiber optic cable strain relief 124 to anelectro-optical module 126 that processes the optical signals inaccordance with the methods described above.

Unlike optical voltage sensors developed for measuring overhead voltage,the modular optical voltage sensor device 100 requires significantcomponent modifications to enable function with a right angle bend inthe pick-off rod of a switchgear elbow. For example, the modular opticalvoltage sensor device 100 for use in either an elbow or T-typeconfiguration requires a more compact body versus overhead sensors, sothat it can be accommodated in underground and switchgear situations.

Additionally, modifications must be made to the optical fibers in orderto be usable with the right angle bends of the sensor casing. Thepick-off rod must be made of non-traditional metals, such as bronze,silicon bronze and silicon steels, rather than the metal used intraditional optical voltage sensors, which include stainless steel oraluminum. Finally, components of the modular optical voltage sensordevice 100, including the crystal, the pick-rods, the drip edge, and theoptical fibers, as described below, must be able to easily integratewith existing rubber housings used for sensors with elbow or T-typeconfigurations.

The present technology provides a modular all-optical sensor, fordetecting and measuring voltage or applied electric field, specificallyadapted for use as switchgear, wherein it is likely to be exposed toflooding or high moisture situations. The modularity of the sensordevice allows for it to be easily adapted for use in all elbowconfigurations and T-type configurations available for load break anddead break products. Thus, the modular all-optical sensor of the presentinvention provides a one-size fits all solution for use with switchgearand voltage monitoring in ground-based and underground applications.

The technology disclosed here includes all components needed for amodular all-optical modular voltage sensor, including the crystal, thepick-off rods, a drip edge, and optical fibers, such that saidcomponents can be used with any commercially available rubber elbow orT-type connectors irrespective of size and configuration of the casing.

A key challenge in developing the present switchgear system is the needto ensure environmental stability. This is particularly true when thesystem may be used in underground environments subject to flooding,where corrosion becomes an issue. The optical voltage sensors known inthe art comprise pick off rods made of materials such as stainless steelor iron. While such materials are suitable for above the ground uses,they would rapidly corrode if used for underground applications. Thus,the internal pick off rod 110, as illustrated in FIG. 13, of the presenttechnology requires customization such that the internal pick off rod110 includes a conductive material that is not corrosive. In someexamples, the internal pick-off rod 110, the external pick-off rod 108,and the base cap 103 are constructed of a bronze, silicon bronze, or asilicon steel material, although other non-corrosive conductivematerials may be utilized.

The modular all-optical sensor of the present invention requiressignificant component modifications relative to overhead optical voltagesensors. In addition to using special materials for the pick-up off rod,modifications include features such as modular pick-off rods that canform right angles, as well as a compact body that can be accommodated inunderground and switchgear situations. Finally, components of themodular system, including the optical sensor crystal, the pick-rods, thedrip edge, and the optical fibers must be able to easily integrate withexisting rubber housings used for sensors with elbow or T-typeconfigurations.

FIGS. 14A and 14B show another exemplary embodiment of an opticalvoltage sensor assembly 200 of the present technology that may beutilized in low voltage (i.e. less than 1 kV) applications with thesystem 10 described above. The optical voltage sensor assembly 200includes an input fiber waveguide 201, an input collimator 202, apolarizer 203, a crystal material 204, an analyzer 205, an outputcollimator 206, and an output fiber waveguide 207, although the opticalvoltage sensor assembly 200 may include other types and/or numbers ofelements or components in other combinations. The structure andoperation of the optical voltage sensor assembly 200 is the same asdescribed with respect to optical voltage sensor assembly 12 except asdescribed below. The technology described will have applications at thedistribution bus of a power grid system, at regulator banks forregulating meters, for switching, and at distribution taps forsingle-phase tap meter to residential, end-use industrial, or businessusers. In particular, this example focuses on measuring voltage afterfinal stepdown, and thus has metering applications at all voltages≤1000volts at either 50 or 60 Hz, including the 120 volt, 240 volt, and 480volt levels encountered on global electricity grids.

FIG. 14A is a schematic view the optical voltage sensor assembly 200that may be employed as an electric field sensor. The input opticalfiber waveguide 201 is connected to a light source (not shown) andconnects to the input collimator 202 that is configured to collimate thelight beam delivered from the light source, such as light source 14 asdescribed above.

The light polarizer 203 is positioned between the input collimator 102and the crystal material 204. The crystal material 204 is the same asthe crystal material 26 as described above. One non-limiting example ofthe Pockels crystal material 204 is a Lithium Niobate crystal, althoughother Pockels crystals may be utilized.

A light analyzer 205 is positioned between the Pockels crystal material204 and the output collimator 206, which is connected to the outputoptical fiber waveguide 207. In some examples, such as illustrated inFIG. 14B, the optical voltage sensor assembly 200 includes electrodes208 that directly contact the Pockels crystal material 204. While FIGS.14A and 14B show an example of the optical voltage sensor assembly 200in a linear form, those skilled in the art will understand that otherconfigurations are possible.

In one example operation, the optical voltage sensor assembly 200, asshown in FIG. 14A by way of example, is placed in an electric field,while the input optical fiber 201 carries incoherent, coherent, orpartially coherent light into the input collimator 202, and through thepolarizer 203. The beam of light introduced through the input opticalfiber 201 is thus linearly polarized and enters the Pockels crystalmaterial 204 at a phase angle fixed by the polarizer 203. As the lightpasses through the Pockels crystal material 204 its phase shifts inproportion to the strength or potential of the electric field as ittravels to the analyzer 205. From the analyzer 205 the light travels tothe output collimator 206 and then to the output fiber waveguide 207.The output fiber waveguide 207 may deliver the output light to adetector, such as detector 16 as described above.

In a second example operation, the optical voltage sensor assembly 200,as shown in FIG. 14B, has the electrodes 208 that directly contact thePockels crystal material 204. In this example, the input optical fiber201 carries light into the input collimator 202 and through thepolarizer 203. The beam of light is thus linearly polarized and entersthe Pockels crystal material 204 at an angle fixed by the polarizer 203.As the light passes through the Pockels crystal material 204 its phaseshifts in proportion to the strength of the electrical potential orvoltage applied by the electrodes 208, as it travels to the analyzer205. From the analyzer 205 the light travels to the output collimator206 and then the output fiber waveguide 207. The output fiber waveguide207 may deliver the output light to a detector, such as detector 16 asdescribed above.

FIG. 15A shows another example of a low voltage optical electric fieldsensor 300. In this example, a fiber collimator 301 (this could be aninput or output fiber collimator depending on orientation) is held inplace by a collimator block 302. The collimator block 302 providesmechanical stability and protection for the collimator 301 as itattaches to a glass spacer block 303. The glass spacer block 303surrounds a Pockels crystal material 304 and reduces stress on thePockels crystal material 304. The Pockels crystal material 304 comprisesany crystal material known in the art, and in one non-limiting examplethe Pockels crystal material 304 comprises a Lithium Niobate crystal.

In this example, two conductive electrodes 308 contact the Pockelscrystal 204 and carry a voltage to the Pockels crystal material 204. Theelectrodes 308 may comprise any conductive material known in the art.Non-limiting examples of conductive material that may be used for theelectrodes 308 include metals, such as copper, silver, aluminum, orgold, electro-ceramics, conducting dielectric materials, and conductingfibers, although other conductive materials may be utilized. A prism cap306 lies at the bottom of the low voltage optical voltage sensorassembly 300 and controls polarization properties of light upon totalinternal reflection (TIR) within the prism.

The glass spacer block 303 between the collimator block 302 and thePockels crystal material 304 provides for a uniform and homogeneousoptical interface, reducing thermal mismatch between the crystal and theglass materials. The surfaces of the glass spacer block 303 are flatwith minimal curvature and low surface roughness in order to provideoptimal surfaces for bonding the collimator block 302 assembly with thecollimator 301 and the crystal material 304 thereby integrating theoptical assembly. Bonding the components to the glass spacer block 303minimizes fluctuations due to thermal variation of intrinsicbirefringence in the optical assembly.

FIG. 15B is a more detailed illustration of the low voltage opticalelectric field sensor 300. showing all components described in FIG. 15Aalong with some additional structures, although the low voltage opticalelectric field sensor 300 may include other types/numbers of elements inother configurations. In this example, the low voltage optical electricfield sensor 300 includes a sensor body 307 that provides a non-limitingexample of one potential solution for assembly of the presenttechnology. The sensor body 307 may be comprised of any material knownin the art, including metal, plastic, rubber, carbon composite, orsimilar materials, although other suitable materials may be utilized forthe sensor body 307. The sensor body 307 allows the sensor to beinstalled in various types of electrical boxes or enclosures. Aretroreflecting prism 308 covers the prism cap 306 (FIG. 14A). Theretroreflecting prism 308 provides for a double pass of light throughthe Pockels crystal material 304. The double path length of transmittedlight in turn doubles the sensitivity of the device.

In an exemplary operation of the low voltage low voltage opticalelectric field sensor 300 shown in FIGS. 15A and 15B, light from anincoherent, coherent, or partially coherent source is delivered by theinput fiber collimator 301, inserted into the collimator block 302, andtravels through a polarizer and through the glass spacer block 303. Thebeam of light is thus linearly polarized entering the Pockels crystalmaterial 304 along the direction of the optical axis (b-axis) of thePockels crystal material 304. The polarization state has a non-zeroprojection with the a-axis and c-axis, and ideally for the case ofLithium Niobate is at 45 degrees with respect to the these axes.

The polarized light beam is reflected twice by the specially designedretroreflecting prism 308, and reenters the Pockels crystal material304. Based on the Pockels effect, with an electrical field applied tothe Pockels crystal material 304, such as through the electrodes 308, byway of example, an optical phase is imparted to the light beam, which isthen, in general, elliptically polarized. Upon exiting the Pockelscrystal material 304, the light with imparted optical phase is incidenton the output polarizer, or analyzer. The orientation of the analyzerideally is coincident with the polarization vector of the lightproducing maximum modulation of light associated with the time dependentelectric field applied across the Pockels crystal material 204. ForLithium Niobate in a transverse modulator configuration (equation 8),this corresponds to the semi-major axis of the outgoing ellipticallypolarized light.

The output polarizer or analyzer (in similarity to the input polarizer)can be embedded, bonded, or attached to the output collimator 301,through which the light is fiber-optically coupled as it exits theoptical assembly, or it can also be attached to other portions orcomponents of the optical assembly after exiting the crystal, such asthe collimator block 302.

FIG. 16 shows a top-view perspective of another exemplary low voltageoptical electric field sensor 400. It should be noted that whilereferences will be made to the top and sides of the low voltage opticalvoltage sensor assembly 400, these references are relative to theorientation of the figure, and in no way, limit the orientation ofsensor components in real world applications.

In this example, the low voltage optical voltage sensor assembly 400comprises a case 401 that allows the low voltage optical electric fieldsensor 400 to be easily attached to various surfaces including those ofenclosures. It should be clear to those skilled in the art that the case401 may have any suitable configuration and may be constructed of anysuitable materials.

In this example, an input collimator 402 and an output collimator 403are shown exiting the top of the low voltage optical voltage sensorassembly 400. The input collimator 402 and the output collimator 403 areheld in place by a collimator block 404. In some examples, the inputcollimator 402 comprises a polarizer while in other embodiments apolarizer (not shown) is placed between the input collimator 402 and thePockels crystal material (not shown). Similarly, in some examples, theoutput collimator 403 comprises an analyzer or polarizer while in otherembodiments an analyzer or polarizer (not shown) is placed between theinput collimator 403 and the Pockels crystal material (not shown).Potential carrying electrodes 408 are shown at both sides of the lowvoltage optical voltage sensor assembly 400. These conductive electrodes408 directly contact that Pockels crystal (not shown).

Operation of the low voltage optical voltage sensor assembly 400 of FIG.16 requires that light pass from the input collimator 402 and anypolarizer present into the Pockels crystal material (not shown) and theretro-reflecting prism complex (not shown), such that the collimatedlight passes through the Pockels crystal material (not shown) two timesbefore passing back into the output collimator 403. When a voltagepotential is applied to the electrodes 408, the voltage potential causesa phase shift of light passing through the Pockels crystal material (notshown). The magnitude of this phase shift, known as the Pockels effect,correlates to the voltage potential being applied to the Pockels crystalmaterial. Thus, when a voltage potential is applied to the electrodes408, and hence the Pockels crystal material, the phase of collimatedlight emanating out of the output collimator 403 will be shiftedrelative to the phase of light at the input collimator 402. By analyzingthe difference in phase of the output light versus the input light, andapplying algorithms, the voltage potential can be determined.

Applications for the present technology include measuring and monitoringvoltage and power in numerous situations where low voltage circuits arepresent (i.e., ≤1000 volts). These applications can include both singleand three phase circuits. Broad examples of applications include use ona distribution bus of a power grid system, a regulator bank as aregulating meter, in switching, and at distribution taps as a single orthree phase tap meter to residential or end-use industrial or businesslines.

Non-limiting examples of uses may include measuring voltage ofelectricity being fed into residential buildings, office buildings,industrial facilities, and electrical vehicle (EV) charging stations.The present technology may also be used by entities outside of theelectrical distribution industry. For example, the examples of lowvoltage sensors described herein may be used to manage energy use withinsmart buildings, within manufacturing facilities, or within otherindustrial complexes. It may also be used in the transportation industryto monitor electricity used for high speed rail, commuter rail, subways,and trams. Other non-limiting uses within transportation could includemonitoring voltage on nautical vessels or aircraft. In addition, thepresent technology can be used in systems that facilitate the control ofelectricity demand. As such it can serve as a component of anintelligent circuit breaker that reacts to load demand (e.g., peakdemand, etc.).

Having thus described the basic concept of the invention, it will beapparent to those skilled in the art that the foregoing detaileddisclosure is intended to be presented by way of example only, and isnot limiting. Various alterations, improvements, and modifications willoccur and are intended to those skilled in the art, though not expresslystated herein. These alterations, improvements, and modifications areintended to be suggested hereby, and are within the spirit and scope ofthe invention. Accordingly, the invention is limited only by thefollowing claims and equivalents thereto.

What is claimed is:
 1. An optical voltage sensor assembly comprising: aninput collimator positioned and configured to collimate an input lightbeam from a light source; a crystal material positioned to receive theinput light beam from the light source and configured to exhibit thePockels effect when an electric field is applied through the crystalmaterial; an output collimator positioned to receive an output lightbeam from the crystal material and configured to focus the output lightbeam from the crystal material onto a detector configured to measure theoptical phase change between the input light beam and the output lightbeam based on the Pockels effect; a temperature sensor configured tomeasure temperature in the area of the optical voltage sensor assembly;and a sensor computing device coupled to the detector and thetemperature sensor, the sensor computing device comprising a processorand a memory coupled to the processor, wherein the processor executesprogrammed instructions stored in the memory to: determine, based on themeasured optical phase change based on the Pockels effect, a voltagedrop across the crystal material; and apply one or more calibrationfactors to the determined voltage drop across the crystal material basedon the measured temperature from the temperature sensor to determine acorrected voltage.
 2. The optical voltage sensor assembly of claim 1,wherein the crystal material is a non-centrosymmetric crystal material.3. The optical voltage sensor assembly of claim 2, wherein thenon-centrosymmetric crystal material is one of crystal point groupsymmetry 3m, 42m, 43m, m3m, 4 mm, 2 mm, or
 23. 4. The optical voltagesensor assembly of claim 1, wherein the crystal material is selectedfrom the group consisting of C₆H₅O₂N,Pb_(0.814)La_(0.124)(Ti_(0.6)Zr_(0.4))O₃ (PLZT), β-Zns, ZnSe, ZnTe,Bi₁₂SiO₂₀, Ba_(0.25)Sr_(0.75)Nb₂O₆, Kta_(0.35)Sr_(0.75)Nb_(0.65)O₃,CsH₂AsO₄, NH₄H₂PO₄, NH₄D₂PO₄, KD₂PO₄, KH₂PO₄, Lithium Niobate (LiNbO₃),LiTaO₃, BaTiO₃ SrTiO₃, Ag₃AsS₃, KNbO₃, and electro-optic polymers. 5.The optical voltage sensor assembly of claim 1, further comprising: aninput linear polarizer positioned and configured to polarize the inputlight beam from the light source; and an output linear polarizerpositioned and configured to polarize the output light beam from thecrystal material.
 6. The optical voltage sensor assembly of claim 5,wherein the input linear polarizer and the output linear polarizer havea thickness of less than about 1.0 mm.
 7. The optical voltage sensorassembly of claim 1 further comprising: a retro-prism device coupled tothe crystal material and positioned to receive light directed from theinput collimator through the crystal material, wherein the retro-prismdevice is configured to redirect the light received through the crystalmaterial back through the crystal material to the output collimator. 8.The optical voltage sensor assembly of claim 1, wherein the temperaturesensor is coupled to a component of the optical voltage sensor assembly.9. The optical voltage sensor assembly of claim 1, wherein thetemperature sensor comprises one of a GaAs bandgap fiber-optictemperature sensor, a fluorescence fiber-optic temperature sensor, anelectrical temperature sensor, or a mechanical temperature sensor. 10.The optical voltage sensor assembly of claim 1 further comprising: apair of electrodes in contact with the crystal material, wherein thepair of electrodes are positioned to provide a voltage potential acrossthe crystal material.
 11. A method for measuring voltage comprising:providing the optical voltage sensor assembly of claim 1; subjecting thecrystal material of the optical voltage sensor assembly to an appliedelectric field; measuring the optical phase change between the inputlight beam and the output light beam based on the Pockels effect; anddetermining the voltage drop across the crystal material based on themeasured optical phase change between the input light beam and theoutput light beam and one or more properties of the crystal material.12. The method of claim 11 further comprising: measuring the temperaturenear the crystal material of the optical voltage using the temperaturesensor; and applying one or more calibration factors to the determinedvoltage drop across the crystal material based on the measuredtemperature to determine the corrected voltage.
 13. The method of claim12, wherein the temperature sensor is coupled to a component of theoptical voltage sensor assembly.
 14. The method of claim 11, wherein thetemperature sensor comprises one of a GaAs bandgap fiber-optictemperature sensor, a fluorescence fiber-optic temperature sensor, anelectrical temperature sensor, or a mechanical temperature sensor. 15.The method of claim 11, wherein the crystal material is anon-centrosymmetric crystal material.
 16. The method of claim 15,wherein the non-centrosymmetric crystal material is one of crystal pointgroup symmetry 3m, 42m, 43m, m3m, 4 mm, 2 mm, or
 23. 17. The method ofclaim 11, wherein the crystal material is selected from the groupconsisting of C₆H₅O₂N, Pb_(0.814)La_(0.124)(Ti_(0.6)Zr_(0.4))O₃(PLZT),β-Zns, ZnSe, ZnTe, Bi₁₂SiO₂₀, Ba_(0.25)Sr_(0.75)Nb₂O₆,Kta_(0.35)Sr_(0.75)Nb_(0.65)O₃, CsH₂AsO₄, NH₄H₂PO₄, NH₄D₂PO₄, KD₂PO₄,KH₂PO₄, Lithium Niobate (LiNbO₃), LiTaO₃, BaTiO₃ SrTiO₃, Ag₃AsS₃, KNbO₃,and electro-optic polymers.
 18. The method of claim 11, wherein theoptical voltage sensor assembly further comprises an input linearpolarizer positioned and configured to polarize the input light beamfrom the light source, and an output linear polarizer positioned andconfigured to polarize the output light beam from the crystal material.19. The method of claim 18, wherein the input linear polarizer and theoutput linear polarizer have a thickness of less than about 1.0 mm. 20.The method of claim 11, wherein the optical voltage sensor assemblyfurther comprises: a retro-prism device coupled to the crystal materialand positioned to receive light directed from the input collimatorthrough the crystal material, wherein the retro-prism device isconfigured to redirect the light received through the crystal materialback through the crystal material to the output collimator.
 21. Themethod of claim 11, wherein the optical voltage sensor assembly furthercomprises: a pair of electrodes in contact with the crystal material,wherein the pair of electrodes are positioned to provide a voltagepotential across the crystal material.